An inkjet printer includes a printing assembly having a printhead, or printheads, to deposit ink onto a print media, such as paper. A printhead has an orifice plate that is formed with nozzles through which ink drops are “fired”, or otherwise ejected, onto the print media to form an image, such as text or a picture. The ink drops dry, or are heated to dry, on the print media shortly after deposition to form the printed image.
There are various types of inkjet printheads including, for example, thermal inkjet printheads and piezoelectric inkjet printheads. For a thermal inkjet printhead, ink droplets are ejected from individual nozzles by localized heating with a heating element located at individual nozzles. An electric current is applied to a heating element which causes a small volume of ink to be rapidly heated and vaporized. The ink expands when heated which causes it to be ejected through the nozzle. A driver circuit is coupled to individual heating elements to provide the energy pulses and thereby controllably deposit ink drops from associated individual nozzles. The drivers are responsive to character generators and other image forming circuitry to energize selected nozzles of a printhead for forming images on the print media.
A conventional inkjet printer has a print unit that includes a reciprocating inkjet pen carriage system for travel back and forth across a print zone along an axis that spans a print media, or otherwise spans a printing width. A reciprocating inkjet pen can be passed over the same section of an image in a print area to provide redundant printing and improve printed image quality. With the advent of fixed page wide array printbar assemblies having multiple printheads that span the width of a print media, or otherwise span a printing width, there is a need for print unit configurations that provide a similar printing redundancy to improve printed image quality.
Paper cockle can occur when print media becomes wet from the ink being deposited onto the media, causing the print media to expand and become wavy having an uneven appearance, particularly when different areas of the media expand at different rates and in different amounts. Typically, ink applied by a thermal inkjet to form an image on a print media is 70-80% water which is the medium used to boil the fluid and disperse the ink. Drying the ink with a heater after it has been deposited onto the print media removes, or otherwise dissipates, the water from the ink before it soaks into the fibers and expands the print media.
Another factor that adds to paper cockle in some printers is the application of chemical compounds known as “fixers.” Fixers are colorless transparent compounds that are applied to the print media either before or after the ink is deposited to help prevent smearing of an image, sharpen images such as edges of letters, enhance colors, and the like. Water is the vehicle by which fixers are applied by a thermal inkjet to a print media which adds to the excess of moisture. However, fixers not only add more moisture to a print media, but when a fixer is applied, more ink can be required to produce an acceptable optical density of the colors which adds even more moisture to some areas of the print media. This causes a greater likelihood of paper cockle.
With page wide array printbar assemblies, a greater quantity of ink can be deposited onto a print media at a faster rate than with a conventional inkjet printer having a reciprocating inkjet pen carriage system. When a greater quantity of ink is deposited in less time, the print media is more susceptible to paper cockle, and more powerful heaters are required to dry the ink. Additionally, more heat for a drier media can be required for post processing the print media, such as with page trimmers, folders, booklet makers, laminators, and the like. More heat from more heaters, however, can degrade the quality of the printheads and nozzles through which the ink is deposited onto the print media. Accordingly, print unit configurations are needed to dissipate greater quantities of moisture from ink that is applied at a faster rate while maintaining the integrity of the printheads and nozzles that deposit the ink.